For BPF_RSH | BPF_K, it could be implemented using NFP direct shift
instruction. For the other BPF_X shifts, NFP indirect shifts sequences need
to be used.
Separate code-gen hook is assigned to each instruction to make the
implementation clear.
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com> Signed-off-by: Jiong Wang <jiong.wang@netronome.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org>